the first thing i noticed that would be a no-contact for me is this "I recently changed my playstyle from punk to post-hardcore/metalcore. I've had a lot of influence from these genres so I'm settling on this as what I want to play..."
i find this very offputting and wouldn't call a musician who put this in their ad. the rest of the bandmix stuff seems pointless to me. the list of gear, the frequency you practice? i don't care and don't want to hear about it, but i realize that's a bandmix thing.
have you considered linking to samples of your playing?
most of my ads to find people to jam with or to form bands were on craigslist. i'm in l.a. and heard from tons of musicians, but while i prefer punk and harder types of metal, i'm open to a lot more styles of music, and heard from people in every genre i can think of. we also have a local facebook musician group that's very active and pretty well-vetted. i wouldn't even think of checking for musicians on bandmix nor do i have an account there.
i also tend not to want to join bands with folks under 21 because some clubs don't want to let them in due to legal annoyances. my buddy was invited to join a then up-and-coming 19 year old singer, and the clubs they did play at had the singer come in different doors or keep track of them. the band couldn't really hang out at the club to support other acts as they wanted to support the singer, who wasn't yet legal drinking age.
meeting people at jam nights is useful, but none around me let under-21 year olds in. our guitar centers have bulletin boards back by the restrooms with listings for bands looking for members.
best of luck finding a band to join or start.
She pretty much nailed it there, and said almost everything I thought while reading your ad. The 2 things that jumped out the most were the 20 year old thing, and that first part about changing your play style. I'm not even sure what that really means, and it would be off putting to me.
I'll pile it on a bit, too
... but my intent is good...
For the style of band you're looking to jump into, your picture is not helpful. IMO. Looks like you're a good looking guy, but that pic makes you look very young and honestly - a bit too harmless for hardcore. I'd take a crapload of pictures and then ask others opinions and find one that gives you just a little more edge. I believe you have what it takes to get a killer picture to post. Even if it were just your face, with no expression. Again... only my opinion on that.
Last, but most importantly, the best way to get out there playing is to be willing to play just about anything - with anyone. You gain experience that way and get to meet lots of people. Getting into a band isn't like getting married. You don't have to be monogamous about it, and you can keep searching for exactly what you want, while playing with others. Your tastes might very well change in time, and you might very well start collaborating with others and coming up with awesome new material.
When my band The Nerve started, I was a punk guy and the other songwriter (the guitarist) came from a Rush tribute band. We couldn't be further apart in what we REALLY wanted to be playing, but we both influenced each other lots. And it turned into an awesome thing.
Hope that helps some. And just in case it sounds like I'm not, I AM on your side
. I like to see people succeed.
- and meet some people. Show up as a fan, be friendly let people get to know you and if you're a decent guy who's fun to hang out with you'll get what you want. 
